Gearbox - Coursework on machine parts

Contents

Introduction

1 Motor selection and kinematic calculation

2 Determination of power and transmitted torques

3 Calculation of gears

3.1 Calculation of conical gear with straight tooth of high-speed gearbox stage

3.2 Calculation of cylindrical helical transmission of low-speed gearbox stage

3.3 Calculation of chain transmission

4 Preliminary calculation of shaft diameters

5 Selection and check calculation of couplings

5.1 Elastic bushing-finger coupling

5.2 Cam coupling

6 Preselection of bearings

7 Layout diagram and selection of lubrication method of gears and bearings, sizing of housing parts

8 Calculation of shafts by equivalent moment

8.1 Check calculation of drive shaft

8.2 Check calculation of intermediate shaft

8.3 Check calculation of driven shaft

9 Calculation of bearings for durability

9.1 Calculation of driving shaft bearings

9.2 Calculation of intermediate shaft bearings

9.3 Calculation of driven shaft bearings

10 Selection and check calculation of key connections

11 Assigning fits, surface roughness, selecting degrees of accuracy, and assigning feature control tolerances

12 Calculation of shafts for endurance

12.1 Calculation of driving shaft

12.2 Calculation of intermediate shaft

12.3 Calculation of driven shaft

13 Calculation of control mechanisms

14 Description of box assembly

15 Adjustment of bearings and engagement

15.1 Adjustment of gears

15.2 Adjustment of bearings

16 Description of the wiring diagram. Assembly and adjustment of the drive

Literature

Introduction

A reduction gear is a mechanism consisting of gear or worm gears, made in the form of a separate element and serving to transfer rotation from the shaft of the engine to the shaft of the working machine.

The purpose of the reduction gear is to reduce the angular speed and increase the torque of the driven shaft compared to the driving one.

The use of gearboxes is due to economic considerations. The mass and cost of the engine at the same power decrease with an increase in its speed. It turns out that the use of high-speed downshift engines instead of a slow-speed engine without transmission is economically feasible. Asynchronous motors with a frequency of 750 and 1500 rpm are most widely used.

The reduction gear consists of a housing in which transmission elements are placed - gears, shafts, bearings, etc.

Gearboxes are classified according to the following main features: gear type (toothed, worm or gear-worm); number of stages (single-stage, two-stage, etc.); type of gears (cylindrical, conical, etc.); relative location of shafts in space (horizontal, vertical); peculiarities of kinematic scheme (unfolded, coaxial, with bifurcated stage, etc.). In this project, a two-stage conical cylinder reverse gearbox is being developed.

Gears are the main type of gear in mechanical engineering. Their main advantages: high load capacity, and, as a result, small dimensions; high durability and reliability of operation; high efficiency; constant transmission ratio; possibility of application in a wide range of powers, speeds, transfer ratios. Disadvantages: noise during operation, inability to continuously change the gear ratio, insecurity during overloads, the possibility of significant dynamic loads due to vibration.

Bearings serve as supports for shafts. They receive radial and axial loads applied to the shaft and maintain a predetermined position of the shaft rotation axis. This gearbox uses radial-thrust ball bearings, radial-thrust roller bearings, as well as radial ball bearings that receive radial and axial loads in conical and cylindrical gears.

Box Assembly Description

Prior to assembly, inner cavity of box body is thoroughly cleaned and covered with oil-resistant paint. Assembly is carried out in accordance with the drawing of the general view of the box, starting from the shaft assemblies:

- a coupling 17, bushings 15 are installed on the splines of the high-speed shaft 9, in which keys 57 are put and gears 14 are put, after which a bushing 16 is installed on the shaft and bearings 45 and 47, previously heated in oil to 80100 ° C, the bearing 47 is fixed with a locking ring 41 ;

- heated bearings 46 are pressed onto intermediate shaft-gear 21, tightened by nuts 18 with washers 59, after which wheel of conical gear 20 is installed, fixed in axial direction by washer with bolt 33;

a gear wheel 29 is mounted on the slow-moving shaft 30, and then a sleeve 28 and bearings 48 preheated in oil are mounted.

Assembled shafts are laid in base of case 3 and cover of case 4 is put on, covering preliminary surfaces of cover and case joint with alcohol varnish. Conical pins 58 are used to base the cover relative to the housing. Then install bearing covers 10,19,25,26 with gaskets 11 and 24. By turning the shafts there is no jamming of the bearings (the shafts must be rotated by hand) and the covers are fixed with screws 34.

Then plug of oil discharge hole 5 with gasket 6 and plug of level 7 are screwed in. Oil is poured into the housing and the inspection hole is closed with a cover-perfume 2 with a pad made of cardboard 8; and securing the cover with screws 32.

The assembled box shall be rolled and tested on the bench according to the program specified in the specifications.

Adjustment of bearings and hooks

15.1 Adjustment of gears

To adjust the gears, it is necessary to shift the entire set of shafts with gears in the axial direction until the middle plane of the wheel coincides with the axis of the gear. This is achieved by transferring a portion of the gaskets 11 and 24 from one side of the housing to the other. In order to maintain the adjustment of the bearings, the total thickness of the set of gaskets must remain unchanged.

To check the correctness of the gear axis relative to the middle plane of the gear, a thin layer of paint is applied to the working surface of the gear, after which imprints are obtained on the teeth of the wheel by turning the shaft, the nature of which is determined by the correctness of engagement.

When gear wheel is displaced, its position is adjusted by setting of gaskets. When properly engaged, the paint shall cover the tooth surface of the wheel by a height of not less than 60% and by a length of not less than 75%.

The centre-to-centre distance shall be checked by measuring the radial clearance which, as for gearing, shall be 0.25 m.

The radial clearance 1 is checked by means of a lead strip embedded in the central cavity of the wheel. Lead strip is laid over entire length of worm wheel recess, after which it is clamped by shaft installed in bearing without its rotation.

Thickness of removed strip is measured by micrometer or caliper.

In the absence of a radial gap, the gear around the periphery of the projections will contact the gearwheel recess, which will cause excessive heating and failure of the gear pair. Excessive clearance also causes incorrect transmission operation.

Adjustment of engagement is performed by changing number of adjusting gaskets of positions 11 and 24 installed between housing of positions 2 and 3 and bearing covers of positions 10, 19, 25, 26.

First, all shaft assemblies of the box must be assembled. Install them in the base of the housing. Put the housing cover on the base. Install bearing covers with gasket sets.

Next, you should check the rotatability of the shafts. They must rotate without knocking and jamming. If necessary, move a number of gaskets from under one bearing cover under the opposite one.

Having achieved the required smoothness of rotation of the shafts, it is necessary to remove the cover of the housing and paint all the teeth of the larger wheel of the first stage with special paint. The housing cover and bearing covers must then be put on. Further, it is necessary to turn the input shaft of the box so that the larger wheel of the first stage makes a complete revolution. Now check the contact spot on the smaller wheel of the first stage. It should be at least 75%.

The same operation must be carried out for the wheels of the second stage.